Driven by direct and indirect legislations, electrification will be required for compliance in the future automotive world. For hybrid and electric vehicles, heat pump systems represent a proven solution to extend the driving range of electrified vehicles and hold significant potential in meeting the increasing demands on electrification. Compared to heating methods using high voltage positive temperature coefficient (HV-PTC) heaters or phase-change material (PCM) heat storage, for example, a heat pump system may extend the driving range by up to 30% (FTP drive cycle at −10 □C; supplier data).
The commonly used air-to-air heat pump systems demonstrate the highest energy efficiency. Such systems, however, involve sophisticated controls and increase costs due in part to the addition of refrigerant valves. Even more, there are certain potential safety risks associated with such systems that circulate refrigerant through cabin heat exchangers. In the event of an evaporator breach when the natural refrigerant R744 (carbon dioxide) is used, for example, such a breach could pose health threats to occupants due to elevated levels of CO2 concentration in the passenger compartment.
Secondary loop heat pump systems, on the other hand, provide a relatively simple architecture that supports simpler controls and is cost effective. Overall, potential safety risks are minimized because no refrigerant is circulated through cabin heat exchangers. In addition, a secondary loop heat pump typically uses less refrigerant charge than a similar size air-to-air heat pump. This could represent a significant cost saving for R1234yf systems where the refrigerant itself is relatively expensive. While these systems overcome many of the noted issues associated with other systems, secondary loop systems are generally less efficient due primarily to heat transfers occurring indirectly between ambient air and passenger compartment air.
Given the noted and distinct advantages of secondary loop heat pump systems, a need exists for such a system that is capable of dynamic, adaptive control for improved energy efficiency. Such a system might may be sufficient to eliminate HV-PTC heaters for the passenger compartment and HV-PTC heaters for warming vehicle components (e.g., one or more batteries) making such systems a more competitive solution for use in vehicle climate control and thermal management.